The invention is based on a fuel injection nozzle for internal combustion engines, in particular a cold-starting valve whose valve needle opens counter to the force of a closing spring. The valve needle is also urged in the closing direction by an additional force, via an adjusting piston exposed either to the delivered fuel or to a control pressure.
In order to control the opening-stroke movement of the valve needle in fuel injection nozzles, it is known to provide an adjusting piston which on one end has a stop cooperating with the valve needle and on the other end is exposed, for example, to the fuel which is under pressure. An adjusting piston of this kind then acts as a hydraulic pre-stroke limiter; depending on the pressure of the fuel acting on the valve needle, the adjusting piston is temporarily capable of blocking the stroke movement of the needle. However, since its diameter is smaller than that of the valve needle or may be dimensioned as such, then depending upon the fuel supply output the resistance of the adjusting piston is overcome when a higher pressure is attained, and the valve needle is displaced further, for example in order to open up additional injection ports (German Offenlegungsschrift No. 27 11 902 and German Offenlegungsschrift No. 27 11 389).
The undamped movements of the adjusting piston can have the effect of increasing wear; also, at the end of injection when pressure is necessarily relieved, there is no specifically defined position for the adjusting piston, which if a hollow space forms could possibly even be sucked into the pressure line, which can result in lengthening the pre-stroke. At the onset of injection, the relative movements of the piston and the nozzle needle produce unstable behavior on the part of the system as a whole.
There is accordingly a need for a fuel injection nozzle where there are no problems associated with the support of the adjusting piston, in order generally to improve efficiency and eliminate instability and wear.